Night owls : over a three-week period it’s possible to shift the circadian rhythm – improve performance, eating habits, decrease depression and stress


A simple tweak to the sleeping patterns of ‘night owls’ – people with extreme late sleeping and waking habits – could lead to significant improvements in sleep/wake timings, improved performance in the mornings, better eating habits and a decrease in depression and stress.

New international research by the Universities of Birmingham and Surrey in the UK, and Monash University in Australia, showed that, over a three-week period, it was possible to shift the circadian rhythm of ‘night owls’ using non-pharmacological and practical interventions.

The study, published in Sleep Medicine today (INSERT DATE), showed participants were able to bring forward their sleep/wake timings by two hours, while having no negative effect on sleep duration.

In addition, participants reported a decrease in feelings of depression and stress, as well as in daytime sleepiness.

“Our research findings highlight the ability of a simple non-pharmacological intervention to phase advance ‘night owls’, reduce negative elements of mental health and sleepiness, as well as manipulate peak performance times in the real world,” lead researcher Dr. Elise Facer-Childs from Monash University’s Turner Institute for Brain and Mental Health said.

‘Night owls’ are individuals whose internal body clock dictates later-than-usual sleep and wake times – in this study participants had an average bedtime of 2.30am and wake-up time of 10.15am.

Disturbances to the sleep/wake system have been linked to a variety of health issues, including mood swings, increased morbidity and mortality rates, and declines in cognitive and physical performance.

“Having a late sleep pattern puts you at odds with the standard societal days, which can lead to a range of adverse outcomes – from daytime sleepiness to poorer mental wellbeing,” study co-author Dr. Andrew Bagshaw from the University of Birmingham said.

“We wanted to see if there were simple things people could do at home to solve this issue.

This was successful, on average allowing people to get to sleep and wake up around two hours earlier than they were before.

Most interestingly, this was also associated with improvements in mental wellbeing and perceived sleepiness, meaning that it was a very positive outcome for the participants.

We now need to understand how habitual sleep patterns are related to the brain, how this links with mental wellbeing and whether the interventions lead to long-term changes.”

Twenty-two healthy individuals participated in the study. For a period of three weeks participants in the experimental group were asked to:

  • Wake up 2-3 hours before regular wake up time and maximise outdoor light during the mornings.
  • Go to bed 2-3 hours before habitual bedtime and limit light exposure in the evening.
  • Keep sleep/wake times fixed on both work days and free days.
  • Have breakfast as soon as possible after waking up, eat lunch at the same time each day, and refrain from eating dinner after 7pm.

The results highlighted an increase in cognitive (reaction time) and physical (grip strength) performance during the morning when tiredness is often very high in ‘night owls’, as well as a shift in peak performance times from evening to afternoon.

It also increased the number of days in which breakfast was consumed and led to better mental well-being, with participants reporting a decrease in feelings of stress and depression.

“Establishing simple routines could help ‘night owls’ adjust their body clocks and improve their overall physical and mental health.

Insufficient levels of sleep and circadian misalignment can disrupt many bodily processes putting us at increased risk of cardiovascular disease, cancer and diabetes,” Professor Debra Skene from the University of Surrey said.

Dr. Facer-Childs said ‘night owls’, compared to ‘morning larks’, tended to be more compromised in our society due to having to fit to work/school schedules that are out of sync with their preferred patterns.

“By acknowledging these differences and providing tools to improve outcomes we can go a long way in a society that is under constant pressure to achieve optimal productivity and performance,” she said.

This intervention could also be applied within more niche settings, such as industry or within sporting sectors, which have a key focus on developing strategies to maximise productivity and optimise performance at certain times and in different conditions.

It has long been recognized that shift work has a negative impact on health and well-being.

Historically this has been attributed to adverse effects of long work hours, nighttime light exposure, and psychosocial factors – effects that are still recognized as relevant for tolerance to shift work [1,2].

However, the health consequences of shift work should first be understood in terms of a fundamental misalignment between the circadian (i.e., near-24-hour) rhythm of the endogenous biological clock and the timing of the sleep/wake cycle [3].

While this paper is concerned primarily with the long-term health consequences of shift work, the implications of circadian misalignment between the biological clock and the sleep/wake cycle are perhaps best illustrated by how such misalignment increases the risk of workplace accidents and injuries.

In healthy, non-shift workers with normal sleep patterns, daytime wakefulness is driven by the biological clock, which produces circadian rhythmicity driving increased alertness during the daytime and decreased alertness during the nighttime [4,5].

This circadian process is counteracted by a homeostatic pressure for sleep, which builds across waking hours [6,7].

When working during daytime hours, these two processes function in concert and in synchrony with the environmental light/dark cycle to maintain alertness while awake and at work, while allowing for consolidated sleep during the night.

Working nights or early morning shifts means that an individual must be awake when the circadian drive for alertness is low and asleep when it is high, in opposition to the natural biological rhythm.

This leads to shortened and disrupted sleep, and excessive sleepiness while awake [8,9].

This in turn yields increased errors in the workplace, greater risk of accidents and injuries, and degraded health [10,11].

Society is increasingly dependent on around-the-clock operations that require shift work. Many industries and services rely on a continuous workforce, including manufacturing, energy production, transportation, healthcare, law enforcement, and the military.

Based on data collected in the US in 2004 (the last time such data were comprehensively collected), the protective services (police, fire, correction services) have the highest percentage of night and rotating shift workers of any occupation (24.8%), followed by healthcare providers (10.9%) [12].

Such workers, when assigned night shifts, early morning shifts or rotating shifts, must modify their sleep schedules from the normal nighttime hours, placing the individuals into a condition of circadian misalignment.

In 2004, out of more than 15 million US employees working full time on shift or irregular schedules, 5.7 million worked schedules requiring work hours that displace sleep and force wakefulness to be misaligned with the natural circadian rhythm [12]. Given this relatively high prevalence, it is important to understand the impact of circadian misalignment resulting from shift work on workers’ health.

In this paper, we review short- and long-term biological effects associated with displacing the sleep/wake cycle. We also discuss the role of psychosocial factors in the expression of these effects and their impact on health and well-being.

There is a wide range of medical conditions potentially caused or influenced by shift work, and an exhaustive overview of the literature in this area is beyond the scope of the paper. Rather, we focus on four broad health domains that illustrate important components of the health consequences of shift work: metabolic health, risk of cancer, heart health, and mental health, as illustrated in Figure 1.

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Figure 1
Human pathophysiology due to shift work. In this paper, we discuss four broad components of health that are adversely affected by circadian misalignment due to shift work: heart health (top left quadrant), metabolic health (top right quadrant), cancer risk (bottom right quadrant), and mental health (bottom left quadrant). The inner circle represents biological systems that are disturbed by circadian misalignment, and the outer area represents broad psychosocial factors that interact with these disturbed biological systems. The ring between them illustrates key medical conditions that may arise from the interaction, for which shift workers are at elevated risk.

Metabolic Health

Sleep displacement and altered meal timing due to shift work disturb hormonal balance—including key regulators of satiety and hunger, the hormones leptin and ghrelin, respectively [13]. Leptin reduces appetite and signals for the cessation of food intake.

In addition to showing transient increases after meals, leptin levels display a circadian rhythm driven by the biological clock [13].

Ghrelin is a short-acting hormone that stimulates appetite. Ghrelin levels decrease after meals and normally display a reverse diurnal pattern from leptin [14].

Ghrelin levels are related to time fasting (i.e., time between meals) and have a central role in mediating food-seeking behavior and motivation, food intake, and body weight [15,16,17].

Under normal circumstances, ghrelin and leptin work in concert to regulate feeding behavior with appropriate meal timing, size, and nutrients.

However, in shift workers, meal times must be altered in accordance with the displaced sleep/wake schedule, which disrupts the coordination between leptin and ghrelin and dysregulates downstream biological systems related to diet, weight, and metabolism.

Laboratory studies focused on the immediate effects of circadian misalignment have demonstrated decreased leptin levels [13,18] and blunted post-meal suppression of ghrelin [19].

If findings from laboratory sleep restriction studies generalize to shift work, then this may be expected to promote weight gain through enhanced appetite for calorie-dense foods with high carbohydrate content [20], consumption of food at night, and increased caloric intake overall [21].

Indeed, night shift workers tend to have significantly higher body mass index (BMI) and greater waist-to-hip ratio than day shift workers [22,23,24].

Sleep displacement and altered meal timing due to shift work also disturb glucose metabolism [25], through mechanisms that have yet to be elucidated.

In mice, chronic advances of meal time appear to induce insulin resistance, while chronic delays appear to elevate blood glucose levels [26].

In humans, presumably as a long-term consequence of altered glucose metabolism, shift work is associated with increased risk of type II diabetes [27,28].

Deteriorating glycemic control and glucose intolerance are also associated with shift work [29,30,31]. For long-term shift workers (>10 years), the increased risk of diabetes persists into retirement [28].

Exacerbating this problem is that night shift workers tend to crave calorie-dense foods with high carbohydrate content while on shift [32]. All-night fast food restaurants, vending machines, and institutional dining facilities cater to this by serving predominantly processed and fried foods.

The increased diabetes risk may be further amplified by unhealthy changes in lifestyle associated with shift work (e.g., smoking, alcohol consumption, and lack of exercise) [33].

Metabolic syndrome and diabetes risk may be further increased by the timing of eating and food digestion being out of sync with peripheral oscillators in the liver [34] and gut [35].

Over the long run, physiological maladaptation to eating at abnormal circadian times is associated with developing metabolic syndrome (MetS) [36,37,38]. Working at night has been estimated to increase the risk of developing MetS by more than 50% [37].

Although moderators such as diet, exercise, and body weight are important, the evidence of a general connection between shift work and poor metabolic health is strong.

There is some emerging evidence that long-term exposure to sleep displacement alters the composition of the gut microbiota (i.e., the bacteria in the gastrointestinal tract) [39]. Recent work indicates that the gut microbiome shows diurnal variations that are influenced by meal times and disturbed by circadian misalignment [40].

The gut microbiome both responds and contributes to host energy balance, and disruption is associated with inflammation, insulin resistance, and adiposity [41].

Disrupted rhythmicity in the gut microbiome may be involved in an immediate and frequently reported, yet hitherto poorly understood, effect of shift work, namely, gastrointestinal discomfort [42,43].

Dysfunction of the gastrointestinal tract may also explain the significantly higher rate of ulcers in night workers compared to day workers [44], and may have impactful consequences for shift workers’ long-term health.

More information: Facer-Childs et al (2019). ‘Resetting the late timing of ‘night owls’ has a positive impact on mental health and performance,’ Sleep Medicine.

Journal information:Sleep Medicine

Provided by University of Birmingham


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